A lith material is prepared by coating on a support a silver halide photographic emulsion having high contrast. When the material is processed with a special supercontrasy developing solution (, which is called a lith developer hereinafter), it produces a halftone dot or line image with very high contrast. The resultant material can be used as a photographic master for printing.
The term lith developer means a so-called infectious developer in which generally contains a dihydroxybenzene type developing agent and a sulfite as preservative in an amount controlled to about 5 g or less per 1 liter of the developer. During the development process the dihydroxybenzene type developing agent is successively activated and therethrough, development proceeds rapidly to produce an image with very high contrast.
Development of this kind suffers from the defect that it requires time to commence the blackening reaction (, that is, development proceeds slowly at the initial stage), or in contrast with this, at the final stage of development, though density of blackened area remains approximately constant, the image contrast begins to decrease resulting in deterioration of image quality, particularly quality of halftone dots.
It would be very beneficial to the graphic art to obtain sufficient high sensitivity and good image quality (, particularly high contrast and high blackening degree) at all times over a wide period of developing time from the initial stage to the final one of the development, by accelerating the developing speed at its initial stage and by preventing deterioration of image qualities at the final stage of development as much as possible. To obtain these results various accelerating agents for lithographic development have been proposed. For example, alkylamino compounds having arylureas incorporated in lith materials are known as effective accelerating agents for lithographic development. However, such known lithographic development accelerating agents are not desirable because they are slightly eluted from the lith materials in which they are incorporated. Accordingly, they accumulate little by little in the lith developer as the period of using the lith developer increases and cause variations in the sensitivities of lith materials to be processed latter. In view of this problem it has become desirable to determine compounds which exhibit a lithographic development accelerating effect without exhibiting the elution and accumulation phenomenon in the lith developer used.
Lith developers are presently divided broadly into two groups; one group includes those containing as preservatives diethanolamine or triethanolamine (, which are described using the general term amines hereinafter) and the other group includes those not containing such amines in addition to a conventionally used sulfite. Lith developers containing amines are described in, for example, U.S. Pat. Nos. 1,925,557; 2,388,816 and 3,573,914: published examined Japanese Patent Application No. 27346/71: and published unexamined Japanese Patent Application No. 39947/75. However, according to our finding, lith developers containing amines have a tendency to increase the apparent sensitivity, unlike the lith developers not containing amines. This finding implies that amines accelerate the development. This is not desirable because though the same lith materials are used, photographic characteristics attained are subject to variation according to the developer used, that is, whether it contains amines or not. In view of these problems it would be desirable to provide a lith material such that when the same materials are processed with different lith developers they always exhibit generally equal photographic characteristics, being independent of the presence of amines in the developer used.